Coaxial overvoltage protectors consisting of a coaxial line section connected in parallel with a short-circuit line, typically a .lambda./4 short-circuit line, are known in the art. Such conventional overvoltage protectors have a very small bandwidth. Even with a VSWR of 1.1, only a relatively small bandwidth of 20% can be realized. A greater bandwidth can only be attained if the characteristic impedance Z.sub.k of the short-circuit line segment is made larger than the characteristic impedance Z.sub.o of the coaxial line section. However, Z.sub.k cannot be made arbitrarily large, because the remaining received residual spurious voltage is proportional to Z.sub.k. However, if an open-circuit line segment is connected in series with a parallel circuit consisting of the coaxial line section and the short-circuit line, then a bandwidth of about one octave can be achieved with a VSWR of 1.1 (corresponding to a reflection coefficient of approximately 0.05) near the edges of the transmission region.
An overvoltage protector of this type, however, has limited use if two narrow frequency bands are to be transmitted over the line and the center frequencies of the two frequency bands are spaced far apart, for example by one octave. This applies in particular to mobile communication applications where the signals of, for example, the D-network (890 to 960 MHz) and of the E-network (1710 to 1880 MHz) are transmitted to the antenna of the base station over a common antenna cable.